Channel estimation method operable to cancel a dominant disturber signal from a received signal

ABSTRACT

A processing module produces improved main channel estimate. This process involves initially estimating the channel impulse response. This result is based on and combined with a known sequences such as that provided by training sequences of the midamble within RF bursts. From this combination, it is possible to produce an estimated signal from a convolution of the channel impulse response and midamble. The estimated signal may be cancelled or subtracted from the received signal to produce a clearer image of the disturber signal. A blind data recovery performed upon the disturber signal. The recovered disturber data may be used as a reference for disturber channel estimation in order to produce a disturber channel impulse response. With the estimated disturber channel impulse response and the recovered disturber data, an estimated disturber signal may be reconstructed and subtracted from the received signal. This allows the cancellation of the estimated disturber signal. Without a clear or dominant disturber signal, a better representation of the main channel impulse response may be produced. This results in more accurate processing of the received RF bursts and improved receiver performance.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/151,029, filed Jun. 13, 2005, which claims priority to U.S.Provisional Patent Application No. 60/657,564 filed on Mar. 1, 2005, andwhich claims priority to U.S. Provisional Patent Application No.60/679,143 May 9, 2005, all of which are incorporated by referenceherein in their entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to cellular wirelesscommunication systems, and more particularly to the cancellation ofinterference associated with received data communications processed by awireless terminal within a wireless communication system.

BACKGROUND OF THE INVENTION

Cellular wireless communication systems support wireless communicationservices in many populated areas of the world. While cellular wirelesscommunication systems were initially constructed to service voicecommunications, they are now called upon to support data communicationsas well. The demand for data communication services has exploded withthe acceptance and widespread use of the Internet. While datacommunications have historically been serviced via wired connections,cellular wireless users now demand that their wireless units alsosupport data communications. Many wireless subscribers now expect to beable to “surf” the Internet, access their email, and perform other datacommunication activities using their cellular phones, wireless personaldata assistants, wirelessly linked notebook computers, and/or otherwireless devices. The demand for wireless communication system datacommunications continues to increase with time. Thus, existing wirelesscommunication systems are currently being created/modified to servicethese burgeoning data communication demands.

Cellular wireless networks include a “network infrastructure” thatwirelessly communicates with wireless terminals within a respectiveservice coverage area. The network infrastructure typically includes aplurality of base stations dispersed throughout the service coveragearea, each of which supports wireless communications within a respectivecell (or set of sectors). The base stations couple to base stationcontrollers (BSCs), with each BSC serving a plurality of base stations.Each BSC couples to a mobile switching center (MSC). Each BSC alsotypically directly or indirectly couples to the Internet.

In operation, each base station communicates with a plurality ofwireless terminals operating in its cell/sectors. A BSC coupled to thebase station routes voice communications between the MSC and the servingbase station. The MSC routes the voice communication to another MSC orto the PSTN. BSCs route data communications between a servicing basestation and a packet data network that may include or couple to theInternet. Transmissions from base stations to wireless terminals arereferred to as “forward link” transmissions while transmissions fromwireless terminals to base stations are referred to as “reverse link”transmissions.

Wireless links between base stations and their serviced wirelessterminals typically operate according to one (or more) of a plurality ofoperating standards. These operating standards define the manner inwhich the wireless link may be allocated, setup, serviced, and torndown. One popular cellular standard is the Global System for Mobiletelecommunications (GSM) standard. The GSM standard, or simply GSM, ispredominant in Europe and is in use around the globe. While GSMoriginally serviced only voice communications, it has been modified toalso service data communications. GSM General Packet Radio Service(GPRS) operations and the Enhanced Data rates for GSM (or Global)Evolution (EDGE) operations coexist with GSM by sharing the channelbandwidth, slot structure, and slot timing of the GSM standard. The GPRSoperations and the EDGE operations may also serve as migration paths forother standards as well, e.g., IS-136 and Pacific Digital Cellular(PDC).

In order for EDGE to provide increased data rates within a 200 KHz GSMchannel, it employs a higher order modulation, 8-PSK (octal phase shiftkeying), in addition to GSM's standard Gaussian Minimum Shift Keying(GMSK) modulation. EDGE allows for nine different (autonomously andrapidly selectable) air interface formats, known as Modulation andCoding schemes (MCSs), with varying degrees of error control protection.Low MCS modes, (MCS 1-4) use GMSK (low data rate) while high MCS modes(MCS 5-9) use 8-PSK (high data rate) modulation for over the airtransmissions, depending upon the instantaneous demands of theapplication.

To a cellular telephone operating in a receive mode, co-channel andadjacent channel GMSK/8PSK signals appear as colored noise. In order tobetter receive the information intended for the cellular telephone, thecellular telephone must attempt to cancel these interference signals.Prior techniques for canceling such interference included channelequalization for received symbols. However, existing channelequalization techniques fail to typically remove co-channel and adjacentchannel interference sufficiently. Thus, a need exists for improvementsin interference cancellation.

SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theDrawings, the Detailed Description of the Invention, and the claims.Other features and advantages of the present invention will becomeapparent from the following detailed description of the invention madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings in which likereference numerals indicate like features and wherein:

FIG. 1 is a system diagram illustrating a portion of a cellular wirelesscommunication system that supports wireless terminals operatingaccording to the present invention;

FIG. 2 is a block diagram functionally illustrating a wireless terminalconstructed according to the present invention;

FIG. 3 is a block diagram illustrating the general structure of a GSMframe and the manner in which data blocks are carried by the GSM frame;

FIG. 4 is a block diagram illustrating the formation of down linktransmissions;

FIG. 5 is a block diagram illustrating the stages associated withrecovering a data block from a series of RF bursts;

FIG. 6 is a block diagram illustrating the stages associated withrecovering a voice data from a series of RF bursts;

FIG. 7 is a block diagram illustrating the stages associated withrecovering a burst from a data or voice frame;

FIGS. 8A and 8B are flow charts illustrating operation of a wirelessterminal in receiving and processing a RF burst;

FIG. 9 is a block diagram illustrating components of a multi-branchburst equalization component according to an embodiment of the presentinvention; and

FIG. 10 is a block diagram illustrating components of a burstequalization component according to an embodiment of the presentinvention; and

FIG. 11 is a block diagram illustrating components of a burstequalization component according to an embodiment of the presentinvention; and

FIG. 12 is a functional block diagram illustrating the cancellation of adominant disturber signal from a received signal in accordance with anembodiment of the present invention; and

FIG. 13 is a logic flow diagram illustrating operations to cancel adominant disturber signal from a received signal in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are illustrated in theFIGs., like numerals being used to refer to like and corresponding partsof the various drawings.

Gaussian Minimum Shift Keying (GMSK) modulation systems can be modeledas a single-input two-output system in real domain. This model is avirtual single transmit 2 receive system. Interference cancellationtechniques for multiple antennas can be applied to GMSK systems asprovided by embodiments of the present invention that substantiallyaddresses the above identified needs as well as other needs. The presentinvention provides a multi-branch equalizer processing module operableto cancel interference associated with received radio frequency (RF)burst(s). This multi-branch equalizer processing module includesmultiple equalizer processing branches. One equalizer processing branchis operable to be trained based upon known training sequences andequalize the received RF burst. These results are then further processedand used to train a second equalizer processing branch. The secondequalizer processing branch then equalizes the received RF burst toproduce an output based on canceling the interfering signals thatresults in improved processing of the received RF bursts.

FIG. 1 is a system diagram illustrating a portion of a cellular wirelesscommunication system 100 that supports wireless terminals operating inaccordance with embodiments of the present invention. Cellular wirelesscommunication system 100 includes a Mobile Switching Center (MSC) 101,Serving GPRS Support Node/Serving EDGE Support Node (SGSN/SESN) 102,base station controllers (BSCs) 152 and 154, and base stations 103, 104,105, and 106. The SGSN/SESN 102 couples to the Internet 114 via a GPRSGateway Support Node (GGSN) 112. A conventional voice terminal 121couples to the PSTN 110. A Voice over Internet Protocol (VoIP) terminal123 and a personal computer 125 couple to the Internet 114. The MSC 101couples to the Public Switched Telephone Network (PSTN) 110.

Each of the base stations 103-106 services a cell/set of sectors withinwhich it supports wireless communications. Wireless links that includeboth forward link components and reverse link components supportwireless communications between the base stations and their servicedwireless terminals. These wireless links can result in co-channel andadjacent channel signals that may appear as noise which may be coloredor white. As previously stated, this noise may interfere with thedesired signal of interest. Hence, the present invention providestechniques for canceling such interference in poor signal-to-noise ratio(SNR) or low signal-to-interference ratio (SIR) environments.

These wireless links may support digital data communications, VoIPcommunications, and other digital multimedia communications. Thecellular wireless communication system 100 may also be backwardcompatible in supporting analog operations as well. The cellularwireless communication system 100 may support the Global System forMobile telecommunications (GSM) standard and also the Enhanced Datarates for GSM (or Global) Evolution (EDGE) extension thereof. Thecellular wireless communication system 100 may also support the GSMGeneral Packet Radio Service (GPRS) extension to GSM. However, thepresent invention is also applicable to other standards as well, e.g.,TDMA standards, CDMA standards, etc. In general, the teachings of thepresent invention apply to digital communication techniques that addressthe identification and cancellation of interfering communications.

Wireless terminals 116, 118, 120, 122, 124, 126, 128, and 130 couple tothe cellular wireless communication system 100 via wireless links withthe base stations 103-106. As illustrated, wireless terminals mayinclude cellular telephones 116 and 118, laptop computers 120 and 122,desktop computers 124 and 126, and data terminals 128 and 130. However,the cellular wireless communication system 100 supports communicationswith other types of wireless terminals as well. As is generally known,devices such as laptop computers 120 and 122, desktop computers 124 and126, data terminals 128 and 130, and cellular telephones 116 and 118,are enabled to “surf” the Internet 114, transmit and receive datacommunications such as email, transmit and receive files, and to performother data operations. Many of these data operations have significantdownload data-rate requirements while the upload data-rate requirementsare not as severe. Some or all of the wireless terminals 116-130 aretherefore enabled to support the EDGE operating standard. These wirelessterminals 116-130 also support the GSM standard and may support the GPRSstandard.

FIG. 2 is a block diagram functionally illustrating wireless terminal200. The wireless terminal 200 of FIG. 2 includes an RF transceiver 202,digital processing components 204, and various other componentscontained within a housing. The digital processing components 204includes two main functional components, a physical layer processing,speech COder/DECoder (CODEC), and baseband CODEC functional block 206and a protocol processing, man-machine interface functional block 208. ADigital Signal Processor (DSP) is the major component of the physicallayer processing, speech COder/DECoder (CODEC), and baseband CODECfunctional block 206 while a microprocessor, e.g., Reduced InstructionSet Computing (RISC) processor, is the major component of the protocolprocessing, man-machine interface functional block 208. The DSP may alsobe referred to as a Radio Interface Processor (RIP) while the RISCprocessor may be referred to as a system processor. However, thesenaming conventions are not to be taken as limiting the functions ofthese components.

RF transceiver 202 couples to an antenna 203, to the digital processingcomponents 204, and also to battery 224 that powers all components ofwireless terminal 200. The physical layer processing, speechCOder/DECoder (CODEC), and baseband CODEC functional block 206 couplesto the protocol processing, man-machine interface functional block 208and to a coupled microphone 226 and speaker 228. The protocolprocessing, man-machine interface functional block 208 couples tovarious components such as, but not limited to, Personal Computing/DataTerminal Equipment interface 210, keypad 212, Subscriber IdentificationModule (SIM) port 213, a camera 214, flash RAM 216, SRAM 218, LCD 220,and LED(s) 222. When camera 214 and LCD 220 are present, thesecomponents may support either/both still pictures and moving pictures.Thus, the wireless terminal 200 of FIG. 2 may be operable to supportvideo services as well as audio services via the cellular network.

FIG. 3 is a block diagram illustrating the general structure of a GSMframe and the manner in which data blocks are carried by the GSM frame.The GSM frame, 20 ms in duration, is divided into quarter frames, eachof which includes eight time slots, time slots 0 through 7. Each timeslot is approximately 625 us in duration, includes a left side, a rightside, and a midamble. The left side and right side of an RF burst of thetime slot carry data while the midamble is a training sequence.

RF bursts of four time slots of the GSM frame carry a segmented RLCblock, a complete RLC block, or two RLC blocks, depending upon asupported Modulation and Coding Scheme (MCS) mode. For example, datablock A is carried in slot 0 of quarter frame 1, slot 0 of quarter frame2, slot 0 of quarter frame 3, and slot 0 of quarter frame 3. Data blockA may carry a segmented RLC block, an RLC block, or two RLC blocks.Likewise, data block B is carried in slot 1 of quarter frame 1, slot 1of quarter frame 2, slot 1 of quarter frame 3, and slot 1 of quarterframe 3. The MCS mode of each set of slots, i.e., slot n of each quarterframe, for the GSM frame is consistent for the GSM frame but may varyfrom GSM frame to GSM frame. Further, the MCS mode of differing sets ofslots of the GSM frame, e.g., slot 0 of each quarter frame vs. any ofslots 1-7 of each quarter frame, may differ. The RLC block may carryvoice data or other data.

FIG. 4 generally depicts the various stages associated with mapping datainto RF bursts. Data is initially uncoded and maybe accompanied by adata block header. Block coding operations perform the outer coding forthe data block and support error detection/correction for data block.The outer coding operations typically employ a cyclic redundancy check(CRC) or a Fire Code. The outer coding operations are illustrated to addtail bits and/or a Block Code Sequence (BCS), which is/are appended tothe data. In CS-1, the header and data are coded together using blockcoding and convolutional coding. In non-CS-1 coding schemes, the headerand data information are often coded separately.

Fire codes allow for either error correction or error detection. FireCodes are a shortened binary cyclic code that appends redundancy bits tobits of the data Header and Data. The pure error detection capability ofFire Coding may be sufficient to let undetected errors go through withonly a probability of 2⁻⁴⁰. After block coding has supplemented the Datawith redundancy bits for error detection, calculation of additionalredundancy for error correction to correct the transmissions caused bythe radio channels. The internal error correction or coding scheme isbased on convolutional codes.

Some redundant bits generated by the convolutional encoder may bepunctured prior to transmission. Puncturing increases the rate of theconvolutional code and reduces the redundancy per data blocktransmitted. Puncturing additionally lowers the bandwidth requirementssuch that the convolutional encoded signal fits into the availablechannel bit stream. The convolutional encoded punctured bits are passedto an interleaver, which shuffles various bit streams and segments theinterleaved bit streams into the 4 bursts shown.

FIG. 5 is a block diagram that generally depicts the various stagesassociated with recovering a data block from a RF burst(s). Four RFbursts typically make up a data block. These bursts are received andprocessed. Once all four RF bursts have been received, the RF bursts arecombined to form an encoded data block. The encoded data block is thendepunctured (if required), decoded according to an inner decodingscheme, and then decoded according to an outer decoding scheme. Thedecoded data block includes the data block header and the data.Depending on how the data and header are coded, partial decoding may bepossible to identify data

FIG. 6 is a block diagram that depicts the various stages associatedwith recovering data from a transmitted voice frame. This is similar tothe process described with reference to FIG. 5. Typically a 20millisecond voice frame is transmitted, wherein the first half of the 20millisecond voice frame is transmitted within a first series of RFbursts and the second half of the voice frame is transmitted with asecond series of RF bursts. A series of four RF bursts is shown as beingoff-set by 10 milliseconds from the first voice frame, Voice Frame_(n),wherein the second half of Voice Frame_(n) and the first half of thesubsequent voice frame, Voice Frame_(n+1), are coded and interleavedinto the series of four RF bursts. When the four RF bursts areprocessed, the coded block produced produces a data stream thatcomprises the second half of Voice Frame_(n) and the first half of VoiceFrame_(n+1). The first half of Voice Frame_(n), stored within memory,may be combined with the second half of Voice Frame_(n) to produce thedata associated with a valid Voice Frame_(n).

Re-encoding the data associated with a valid Voice Frame_(n), asdescribed with reference to FIG. 7, may result in an at least partiallyre-encoded data bursts that may be used to train the second equalizerprocessing branch. As previously stated, the first half of the voiceframe recovered from a previous set of RF bursts and the second half ofthe voice frame recovered from the current set of RF bursts are combinedto produce the data associated with a voice frame. This voice frame maybe validated and corrected using cycle redundancy checks in order toproduce a valid voice frame. This valid voice frame may then bere-encoded. However, only the second half of the re-encoded VoiceFrame_(n) is used to partially recreate the burst(s). The second half ofre-encoded Voice Frame_(n) may be segmented and interleaved to produce aseries of partially encoded RF bursts. Since the processing of thesecond half of the Voice Frame_(n+1) has not occurred, the RF bursts areonly partially re-encoded. Since Voice Frame_(n+1) has not beenvalidated, the first half of a re-encoded Voice Frame_(n+1) is notpossible and is not used to recreate the burst(s). The partiallyre-encoded burst(s), based on Voice Frame_(n), taken together with theknown training sequences are operable to better train the secondequalizer-processing branch in accordance with an embodiment of thepresent invention.

FIGS. 8A and 8B are flow charts illustrating operation of a wirelessterminal 200 in receiving and processing a RF burst. The operationsillustrated in FIGS. 8A and 8B correspond to a single RF burst in acorresponding slot of GSM frame. The RF front end, the basebandprocessor, and the equalizer processing module perform these operations.These operations are generally called out as being performed by one ofthese components. However, the split of processing duties among thesevarious components may differ without departing from the scope of thepresent invention.

Referring particular to FIG. 8A, operation commences with the RF frontend receiving an RF burst in a corresponding slot of a GSM frame (step802). The RF front end then converts the RF burst to a baseband signal(step 804). Upon completion of the conversion, the RF front end sends aninterrupt to the baseband processor (step 806). Thus, as referred to inFIG. 8A, the RF front end performs steps 802-806.

Operation continues with the baseband processor receiving the basebandsignal (step 808). In a typical operation, the RF front end, thebaseband processor, or modulator/demodulator will sample the analogbaseband signal to digitize the baseband signal. After receipt of thebaseband signal (in a digitized format), the baseband processor performsblind detection of a modulation format of the baseband signal of step810. This blind detection of the modulation format determines themodulation format of the corresponding baseband signal. In oneparticular embodiment according to the GSM standard, the modulationformat will be either Gaussian Minimum Shift Keying (GMSK) modulation orEight Phase Shift Keying (8PSK) modulation. The baseband processor makesthe determination (step 812) and proceeds along one of two branchesbased upon the detected modulation format.

For GMSK modulation, the baseband processor performs de-rotation andfrequency correction of the baseband signal at step 814. Next, thebaseband processor performs burst power estimation of the basebandsignal at step 816. Referring now to FIG. 11 via off page connector A,the baseband processor next performs timing, channel, noise, andsignal-to-noise ratio (SNR) estimation at step 820. Subsequently, thebaseband processor performs automatic gain control (AGC) loopcalculations (step 822). Next, the baseband processor performs softdecision scaling factor determination on the baseband signal (step 824).After step 824, the baseband processor performs matched filteringoperations on the baseband signal at step 826.

Steps 808-826 are referred to hereinafter as pre-equalization processingoperations. With the baseband processor performing thesepre-equalization processing operations on the baseband signal itproduces a processed baseband signal. Upon completion of thesepre-equalization processing operations, the baseband processor issues acommand to the equalizer module.

The equalizer module, whose operation as a multi-branch equalizer willbe discussed in further detail with reference to FIG. 9 and following,upon receiving the command, prepares to equalize the processed basebandsignal based upon the modulation format, e.g., GMSK modulation or 8PSKmodulation. The equalizer module receives the processed baseband signal,settings, and/or parameters from the baseband processor and performsMaximum Likelihood Sequence Estimation (MLSE) equalization on the leftside of the baseband signal at step 828. As was shown previously withreference to FIG. 3, each RF burst contains a left side of data, amidamble, and a right side of data. Typically, at step 828, theequalizer module equalizes the left side of the RF burst to produce softdecisions for the left side. Then, the equalizer module equalizes theright side of the processed baseband signal at step 830. Theequalization of the right side produces a plurality of soft decisionscorresponding to the right side. The burst equalization is typicallybased of known training sequences within the bursts. However, theembodiments of the present invention may utilize re-encoded or partiallyre-encoded data to improve the equalization process. This may take theform of an iterative process wherein a first branch performs burstequalization and a second module performs a second equalization based onthe result obtained with the first branch over a series of RF bursts.

The equalizer module then issues an interrupt to the baseband processorindicating that the equalizer operations are complete for the RF burst.The baseband processor then receives the soft decisions from theequalizer module. Next, the baseband processor determines an averagephase of the left and right sides based upon the soft decisions receivedfrom the equalizer module at step 832. The baseband processor thenperforms frequency estimation and tracking based upon the soft decisionsreceived from the equalizer module at step 836. The operations of step832, or step 854 and step 836 are referred to herein as“post-equalization processing.” After operation at step 836, processingof the particular RF burst is completed.

Referring again to FIG. 8A, the baseband processor and equalizer moduletake the right branch from step 812 when an 8PSK modulation is blindlydetected at step 810. In the first operation for 8PSK modulation, thebaseband processor performs de-rotation and frequency correction on thebaseband signal at step 818. The baseband processor then performs burstpower estimation of the baseband signal at step 820. Referring now toFIG. 8B via off page connector B, operation continues with the basebandprocessor performing timing, channel, noise, and SNR estimations at step840. The baseband processor then performs AGC loop calculations on thebaseband signal at step 842. Next, the baseband processor calculatesDecision Feedback Equalizer (DFE) coefficients that will be used by theequalizer module at step 844. The process to produce these coefficientswill be described in further detail. This determination when using amulti-branch equalizer will be discussed with reference to FIG. 9 andfollowing. The baseband processor then performs pre-equalizer operationson the baseband signal at step 846. Finally, the baseband processordetermines soft decision scaling factors for the baseband signal at step848. Steps 818-848 performed by the baseband processor 30 are referredto herein as “pre-equalization processing” operations for an 8PSKmodulation baseband signal. Upon completion of step 648, the basebandprocessor issues a command to equalizer module to equalize the processedbaseband signal.

Upon receipt of the command from the baseband processor, the equalizermodule receives the processed baseband signal, settings, and/orparameters from the baseband processor and commences equalization of theprocessed baseband signal. The equalizer module first prepares statevalues that it will use in equalizing the 8PSK modulated processedbaseband signal at step 850. In the illustrated embodiment, theequalizer module uses a Maximum A posteriori Probability (MAP)equalizer. The equalizer module then equalizes the left and right sidesof the processed baseband signal using the MAP equalizer to produce softdecisions for the processed baseband signal at step 852. Upon completionof step 854, the equalizer module issues an interrupt to the basebandprocessor indicating its completion of the equalizing the processedbaseband signal corresponding.

The baseband processor then receives the soft decisions from theequalizer module. Next, the baseband processor determines the averagephase of the left and right sides of the processed baseband signal basedupon the soft decisions (step 854). Finally, the baseband processorperforms frequency estimation and tracking for the soft decisions (step836). The operations of steps 854 and 836 are referred to aspost-equalization processing operations. From step 836, operation iscomplete for the particular RF burst depicts the various stagesassociated with recovering a data block from an RF Burst.

While the operations of FIGS. 8A and 8B are indicated to be performed byparticular components of the wireless terminal, such segmentation ofoperations could be performed by differing components. For example, theequalization operations could be performed by the baseband processor orsystem processor in other embodiments. Further, decoding operationscould also be performed by the baseband processor or the systemprocessor in other embodiments.

FIG. 9 is a block diagram illustrating the structure of one embodimentof a multi-branch equalizer processing module 900 operable to performsingle antenna interference cancellation (SAIC) in accordance withembodiments of the present invention. There are two types of SAICequalizer methods: (1) joint-detection (JD); and (2) blind interferencecancellation (BIC). According to one aspect of the present invention,BIC method is selected. The components illustrated in FIG. 9 may behardware components, software components executed by a processor, e.g.,206 or 208 of FIG. 2, or a combination of hardware components andsoftware components. Multi-branch equalizer processing module 900includes a first equalizer processing branch 902 and second equalizerprocessing branch 904. Derotation block 906 receives In phase (I) andQuadrature (Q) components of a baseband burst. This baseband burstcorresponds to RF burst(s), which were described with reference to FIGS.3-7. Derotation block 906 derotates received I and Q burst samples andproduces I and Q burst samples (“bursts”). In one embodiment, firstequalizer processing branch 902 may include a burst equalizer. Thesesamples may be later equalized in accordance with the embodiments of thepresent invention with other samples making up a data packet, e.g., RLCpacket. The iterative processes of the second equalizer processingbranch may be performed in addition to the burst level equalizationduring certain operating conditions.

Burst equalizers, include I and Q Finite Impulse Response (FIR) filters908 and 910 and Minimum Least Squares Estimation (MLSE) equalizer 912that operate upon each burst received from derotation block 906. Thesecomponents are trained by training module 913 using known TrainingSequence(s) (TS), within the midamble received with each burst.Alternately, these components could be trained over multiple bursts.First equalizer processing branch 902 produces soft decisions whereinmultiple soft decisions represent each data bit prior to decoding. Eachsoft sample is provided to deinterleaver 914 which in turn provides thedeinterleaved soft samples to channel decoder 916. Channel decoder 916decodes a data frame from the soft samples (i.e. the multiple softsample(s) that represent each data bit are decoded by the channeldecoder to produce hard bits after decoding).

The data frame produced by channel decoder 916 may be validated andre-encoded using re-encoder 918 in order to produce re-encoded databits. Interleaver 920 receives the re-encoded data bits to produce are-encoded data burst(s). The re-encoded data burst(s), along with knowntraining sequence(s), may then be used to train second equalizerprocessing branch 310.

Second equalizer processing branch 904 includes a buffer 922 operable tostore multiple bursts in memory as well as an I and Q FIR filters 924and 926, respectively. I and Q filters 924 and 926 are operable to betrained by training module 928 using known training sequence and atleast partially re-encoded bursts. In this way, the second equalizerprocessing branch takes at least partially re-encoded data and knowntraining sequences to train the I and Q RF filters. This results in animproved SNR for the burst(s) processed from buffer 922. After the I andQ filters have been trained and used to process the stored burst(s). Theresults are combined with adder 930. This creates an alternate set ofsoft samples which are provided to deinterleaver 914 and channel Decoder916 to produce an alternate set of data bits.

FIG. 10 may be used to describe the first branch of the multi-branchequalizer of FIG. 9 in more detail. In the case of ideal training, both2-branch linear equalizer (LE) and decision-feedback equalizer (DFE)achieve satisfactory performance improvement compared with theconventional receiver. However, when 26 training symbols are trained touse LE or DFE, the degradation is about 2 dB for a single interferingsignal, and about 5 dB for multiple interfering signals and noise likeenvironments. To overcome this problem, an iterative scheme employingthe multi-branch equalizer of FIG. 9 may be used. The first processingbranch as shown may train feed-forward filters 908 and 910 with 4 tapseach and 4 taps feedback filter DFEs.

FIG. 11 may be used to describe the second branch of the multi-branchequalizer of FIG. 9 in more detail. After channel decoding, the data isre-encoded and used to train 7 tap LEs 924 and 926. The reason to chooseLE for the second branch is because of the inter-frame interleaving. There-encoded bits that relate to a voice frame may only provide half ofthe burst (even data bits). DFEs need consecutive samples for thefeedback filter. In addition, LE is simpler than DFE (MLSE). Otherembodiments that use fully re-encoded bits may chose DFEs over LEs forthe second branch.

FIG. 12 provides a functional block diagram operable to implement achannel estimation algorithm that, in the presence of a single dominantinterfering signal, provides an improved main channel impulse response.Such a response may be used to produce filter coefficients for and trainFIR filters, such as the filters disclosed in FIGS. 9-11. The channelestimation algorithm utilizes the midamble or other known sequencescontained within received in order to produce an estimate of the mainsignal. This estimate may then be canceled or subtracted from thereceived signal in order to process/analyze the disturber or interferingsignal. When the disturber or interfering signal is a single dominantsignal, removing this signal from the received signal provide animproved main channel impulse response and receiver performance. Theimproved channel impulse response that results may be used to provideimproved training of equalizers within all the branches of the equalizerprocessing modules illustrated in FIGS. 9, 10, and 11.

In FIG. 12, input samples are received and supplied to first mainchannel estimator 1202. First main channel estimator 1202 is able toproduce a first main channel impulse response using a known midamble orother like sequences. Midamble estimator 1204 receives first mainchannel impulse response from first main channel estimator 1202, and theknown midamble or other like sequences. These inputs are used toconstruct an estimated main channel impulse response which may besubtracted from the received signal to produce a more accurate depictionof the disturber or interfering signal within the midamble. Thedisturber or interfering signal within the midamble may then be providedto disturber channel estimator 1206 to produce an estimated disturberchannel impulse response. A blind data recovery may be performed withinthe midamble area by blind data recovery module 1208.

For a blind receiver, such as blind data recovery module 1208, one maysuppose that disturber channel has a Delta Impulse Response with phaseshift φ₀. In one embodiment the received signal may be expressed asfollows:Sample(n)=Data(n)·(cos(φ₀)+1i·sin(φ₀))+Noise(n)

where, the maximal likelihood data for any assumed phase shift φ may begiven by the expression:D(n)=sign(cos(φ)·Re(Sample(n))+sin(φ)·Im(Sample(n)))The correlation between received signal and recovered data may be givenby the expression:

$\;{{{Correlation}(\varphi)} = {\sum\limits_{n \in {Midamble}}^{\;}\;{{D(n)} \cdot \left( {{{\cos(\varphi)} \cdot {{Re}\left( {{Sample}(n)} \right)}} + {{\sin(\varphi)} \cdot {{Im}\left( {{Sample}(n)} \right)}}} \right)}}}$or${{Correlation}(\varphi)} = {\sum\limits_{n \in {Midamble}}^{\;}\;{{abs}\left( {{{\cos(\varphi)} \cdot {{Re}\left( {{Sample}(n)} \right)}} + {{\sin(\varphi)} \cdot {{Im}\left( {{Sample}(n)} \right)}}} \right)}}$The maximal likelihood disturber channel phase shift φ_(EST) is suchphase shift that provides the greatest correlation:Correlation(φ_(EST))=maxOne can calculate the correlation for possible disturber phases from 0to π with step Δφ and find phase shift φ_(EST) is such phase shift thatgives correlation maximum. The result recovered data will be given byexpression:DataOut(n)=sign(cos(φ_(EST))·Re(Sample(n))+sin(φ_(EST))·Im(Sample(n)))

The output of blind data recovery module 1208 may be supplied to bothdisturber channel estimator 1206 and disturber signal estimator 1210.Disturber channel estimator 1206 produces a disturber channel impulseresponse that when combined with the output of blind data recoverymodule 1208, that may be used to reconstruct the disturber signal withinthe mid amble region or area of the signal of interest. Thereconstructed disturber signal may then be canceled from the inputsamples or received signal in order to produce signals without a cleardisturber signal. Second main channel estimator 1212 is operable toproduce an improved main channel impulse response, which again may beused by any branch within a multi-branch or single-branch equalizer toimprove the performance of the receiver.

FIG. 13 provides a logic flow diagram illustrating one method to producean improved channel estimation in accordance with an embodiment of thepresent invention. At Step 1300 a number of RF burst(s) are received,which are de-rotated as previously described in Step 1302 to producesamples. In Step 1304, the sampled RF burst is processed with a firstmain channel estimator, as described in FIG. 12 to produce the mainchannel impulse response of Step 1306. The main channel impulseresponse, taken in conjunction with a known midamble or other likesequence associated with the received samples, is processed in step 1308to produce an estimated main signal. Step 1310 subtracts the estimatedmain signal from the received signal or samples. Then, Step 1312performs a blind data recovery on the resultant produced in Step 1310.Both the results of the blind data recovery of 1312 and the differencebetween the received signal and the estimated main signal may beprocessed in Step 1314 to produce the disturber channel impulse responseof Step 1316. The disturber channel impulse response may be used inconjunction with the results of the blind data recovery to produce adisturber signal estimate in Step 1318. The disturber signal estimatemay be subtracted from the received or sampled signals in Step 1320. Theresults of Step 1320 may then be processed with a second main channelestimator to produce an improved a better main channel impulse response.This processing occurs in Step 1322 in order to yield the improved mainchannel impulse response of Step 1324.

In summary, the present invention provides a processing module operableto produce an improved channel impulse response. This process involvesinitially estimating the channel impulse response. This result is basedon and combined with a known sequences such as that provided by trainingsequences of the midamble within RF bursts. From this combination, it ispossible to produce an estimated signal from a convolution of thechannel impulse response and midamble. The estimated signal may becancelled or subtracted from the received signal to produce a clearerimage of the disturber signal. A blind data recovery performed upon thedisturber signal. The recovered disturber data may be used as areference for disturber channel estimation in order to produce adisturber channel impulse response. With the estimated disturber channelimpulse response and the recovered disturber data, an estimateddisturber signal may be reconstructed and subtracted from the receivedsignal. This allows the cancellation of the estimated disturber signal.Without a clear or dominant disturber signal, a better representation ofthe main channel impulse response may be produced. This results in moreaccurate processing of the received RF bursts and improved receiverperformance.

As one of average skill in the art will appreciate, the term“substantially” or “approximately”, as may be used herein, provides anindustry-accepted tolerance to its corresponding term. Such anindustry-accepted tolerance ranges from less than one percent to twentypercent and corresponds to, but is not limited to, component values,integrated circuit process variations, temperature variations, rise andfall times, and/or thermal noise. As one of average skill in the artwill further appreciate, the term “operably coupled”, as may be usedherein, includes direct coupling and indirect coupling via anothercomponent, element, circuit, or module where, for indirect coupling, theintervening component, element, circuit, or module does not modify theinformation of a signal but may adjust its current level, voltage level,and/or power level. As one of average skill in the art will alsoappreciate, inferred coupling (i.e., where one element is coupled toanother element by inference) includes direct and indirect couplingbetween two elements in the same manner as “operably coupled”. As one ofaverage skill in the art will further appreciate, the term “comparesfavorably”, as may be used herein, indicates that a comparison betweentwo or more elements, items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention. Theembodiment was chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto, and their equivalents. Further, it should be understoodthat various changes, substitutions and alterations can be made heretowithout departing from the spirit and scope of the invention asdescribed by the appended claims.

1. An apparatus comprising: a first main channel estimator operable toproduce a main channel estimate from input samples of a communicationsignal; a main signal estimator operable to produce an estimated mainsignal from the main channel estimate and a known sequence; a firstcombiner operable to subtract the estimated main signal from the inputsamples; a data recovery module operable to recover disturber channeldata from an output of the first combiner; a disturber channel estimatoroperable to produce a disturber channel estimate based on the output ofthe first combiner and the recovered disturber channel data; a disturbersignal estimator operable to produce an estimated disturber signal fromthe disturber channel estimate and the recovered disturber channel data;a second combiner operable to subtract the estimated disturber signalfrom the input samples; a second main channel estimator operable toproduce an improved main channel estimate based on an output of thesecond combiner; and an equalizer processing module operable to equalizethe input samples using coefficients determined using the improved mainchannel estimate, the equalizer processing module comprising: a firstequalizer processing branch that is operable to be trained based uponthe improved main channel estimate and to equalize the input samples toproduce first equalized samples; and a second equalizer processingbranch that is operable to be trained based upon the improved mainchannel estimate, the known sequence, and re-encoded data bits and toequalize the input samples to produce second equalized samples.
 2. Theapparatus of claim 1, wherein the improved main channel estimate may beused to train filters within a receiver's equalizer processing modules.3. The apparatus of claim 1, wherein the known sequence is a midamble ofthe communication signal.
 4. The apparatus of claim 1, wherein the knownsequence is a training sequence of the communication signal.
 5. Theapparatus of claim 1, wherein: the first equalizer processing branch isfurther operable to extract data from the first equalized input samples;and the second equalizer processing branch is further operable toextract alternate data from the input samples.
 6. The apparatus of claim1, wherein the input samples include Gaussian Minimum Shift Keying(GMSK) main signal symbols and Eight Phase Shift Keying (8PSK)/GMSKinterfering signal symbols.
 7. An apparatus comprising a Radio Frequency(RF) front end operable to receive an RF burst and to produce inputsamples there from; and a baseband processor coupled to the RF front endand comprising: a first main channel estimator operable to produce amain channel estimate from input samples of a communication signal; amain signal estimator operable to produce an estimated main signal fromthe main channel estimate and a known sequence; a first combineroperable to subtract the estimated main signal from the input samples; adata recovery module operable to recover disturber channel data from anoutput of the first combiner; a disturber channel estimator operable toproduce a disturber channel estimate based on the output of the firstcombiner and the recovered disturber channel data; a disturber signalestimator operable to produce an estimated disturber signal from thedisturber channel estimate and the recovered disturber channel data; asecond combiner operable to subtract the estimated disturber signal fromthe input samples; a second main channel estimator operable to producean improved main channel estimate based on an output of the secondcombiner; and an equalizer processing module operable to equalize theinput samples based upon the improved main channel estimate, theequalizer processing module comprising: a first equalizer processingbranch that is operable to be trained based upon the improved mainchannel estimate and to equalize the input samples to produce firstequalized samples; and a second equalizer processing branch that isoperable to be trained based upon the improved main channel estimate,the known sequence, and re-encoded data bits and to equalize the inputsamples to produce second equalized samples.
 8. The apparatus of claim7, further comprising data extraction circuitry for extracting mainsignal data from the equalized input samples.
 9. The apparatus of claim7, wherein the improved main channel estimate may be used to trainfilters within a receiver's equalizer processing modules.
 10. Theapparatus of claim 7, wherein the known sequence is a midamble of thecommunication signal.
 11. The apparatus of claim 7, wherein the knownsequence is a training sequence of the communication signal.
 12. Theapparatus of claim 7, wherein: the first equalizer processing branch isfurther operable to extract data from the first equalized input samples;and the second equalizer processing branch is further operable toextract alternate data from the input samples.
 13. The apparatus ofclaim 7, wherein the input samples include Gaussian Minimum Shift Keying(GMSK) main signal symbols and Eight Phase Shift Keying (8PSK)/GMSKinterfering signal symbols.
 14. A method for training an equalizerwithin a receiver comprising: producing a main channel estimate frominput samples of a communication signal; producing an estimated mainsignal from the main channel estimate and a known sequence; subtractingthe estimated main signal from the input samples to produce a firstcombined output; recovering disturber channel data from the firstcombined output; producing a disturber channel estimate based on thefirst combined output and the recovered disturber channel data;producing an estimated disturber signal from the disturber channelestimate and the recovered disturber channel data; subtracting theestimated disturber signal from the input samples to produce secondcombiner output; producing an improved main channel estimate based onthe second combiner output; and training an equalizer processing moduleof the receiver using the main channel estimate, including: training afirst equalizer processing branch based upon the improved main channelestimate; and training a second equalizer processing branch based uponthe improved main channel estimate, the known sequence, and re-encodeddata bits.
 15. The method of claim 14, further comprising using the mainchannel estimate to train filters within the receiver.
 16. The method ofclaim 14, wherein the known sequence is a midamble of the communicationsignal.
 17. The method of claim 14, wherein the known sequence is atraining sequence of the communication signal.
 18. The method of claim14, wherein the input samples include Gaussian Minimum Shift Keying(GMSK) main signal symbols and Eight Phase Shift Keying (8PSK)/GMSKinterfering signal symbols.
 19. The method of claim 14, furthercomprising: the first equalizer processing branch equalizing the inputsamples to produce first equalized samples; and the second equalizerprocessing branch equalizing the input samples to produce secondequalized samples.
 20. The method of claim 19, further comprising: thefirst equalizer processing branch extracting data from the firstequalized input samples; and the second equalizer processing branchextracting alternate data from the input samples.